1. Field of the Invention
The present invention relates to a surface-mount air-core coil mainly serving as an inductor for use at a high frequency, an electronic component having the air-core coil, and a communication apparatus having the air-core coil.
2. Description of the Related Art
A surface-mount air-core coil disclosed in the Japanese Examined Utility Model Publication No. 5-39611 has been known. As shown in FIG. 12 and FIG. 13, the air-core coil 80 has a coil body 82 formed by winding a conductive wire 81 spirally except for both ends thereof and mount legs 83 formed by folding both ends toward the inside at right angles. The coil body 82 has a circular shape and the lower surface 82a thereof is positioned on the same surface as the lower surfaces 83a of the mount legs 83. Therefore, the height H and the width L of the air-core coil 80 is equal to the outer diameter of the coil body 82. The horizontal length L1 of the mount legs 83 is set shorter than the width L.
The air-core coil 80 is accommodated into each pocket 87 of a package tape 86 as shown in FIG. 14 and supplied to a mounting line. A drawing nozzle of a mounting machine (not shown) takes the air-core coil out of each pocket and mounts it at the specified position on a board 85.
When air-core coils having various characteristics, including inductance, are manufactured, the air-core coils have minutely different diameters in the coil bodies and the height H and the width L of each air-core coil become different. Since only one type of the package tape 86 is prepared in terms of manufacturing cost, a small air-core coil may be handled inappropriately with the pocket 87 having fixed dimensions. In other words, if the coil is too small in height compared with the depth of the pocket 87, the coil may rotate in the pocket 87 and become upside down, preventing mounting even if it is taken out. If the coil is small in width compared with the width of the pocket 87, the coil may move in the pocket 87. It becomes difficult to take out the coil, and in addition, erroneous mounting may occur due to a movement in position. It is needless to say that this problem can be eliminated if a package tape having a pocket suited to the size of each air-core coil having certain characteristics is manufactured. However, this is difficult to achieve in terms of cost.
As shown in FIG. 13, in the conventional air-core coil 80, the lower surface 82a of the coil body 82 is positioned ideally on the same plane as the lower surfaces 83a of the mount legs 83. Due to manufacturing errors, however, the lower surfaces 82a and 83a are usually not on the same plane. As shown in FIG. 15, for example, if the lower surface 82a is positioned lower than the lower surfaces 83a, one or both of the mount legs 83 may be erroneously soldered to the circuit board 85. Alternatively, one of the mount legs 83 may be soldered and the air-core coil stands on the board 85, which is a so-called tombstone phenomenon. It is inconvenient for the mount legs 83 to have a small length L1 when soldered.
Furthermore, since the coil body 82 has a circular cross section perpendicular to its axis as shown in FIG. 12, when the coil has a large inductance, it becomes large in diameter and the height H also becomes large.
Accordingly, it is an object of the present invention to provide a surface-mount air-core coil having good mountability to a circuit board, an electronic component having this air-core coil, and a communication apparatus having this air-core coil.
Another object of the present invention is to provide a surface-mount air-core coil which neither rotates nor moves in position when accommodated into a pocket of a package tape, an electronic component having this air-core coil, and a communication apparatus having this air-core coil.
Still another object of the present invention is to provide a surface-mount air-core coil which can have a low profile while maintaining the same characteristics, including inductance, an electronic component having this air-core coil, and a communication apparatus having this air-core coil.
The foregoing objects are achieved in one aspect of the present invention through the provision of a surface-mount air-core coil comprising: a coil body formed by winding a conductive wire spirally except for both ends; and mount legs formed by folding both ends of the conductive wire horizontally toward the inside in a direction perpendicular to the axis of the coil body, wherein the lower surfaces of the mount legs are positioned below the lower surface of the coil body, and the length of the mount legs is longer than the width of the coil body.
The surface-mount air-core coil having the above structure is soldered, for example, to a circuit board of an electronic component or a communication apparatus by use of the mount legs. Since the mount legs are positioned below the coil body, the mount legs positively contact the circuit board with the lower surface of the coil body not contacting the circuit board even if the outer diameter of the coil body varies in dimension. Problems, such as defective soldering, soldering prevention, and the tombstone phenomenon, do not occur. In addition, when the length of the mount legs is set longer than the width of the coil body, mountability is improved with the sufficiently long legs.
The height of an air-core coil according to the present invention is equal to the sum of the height (outer diameter) of the coil body and the offset of the mount legs. By adjusting the offsets, coils having different outer diameters according to their characteristics, including inductance, can be manufactured at the same height. Even with coils having different outer diameters, when the length of the mount legs is set to a fixed length which is longer than the widths (outer diameters) of the coil bodies, the coils have the same width irrespective of the outer diameters of the coil bodies. Therefore, coils having different outer diameters can be manufactured with a height and a width which are suited to the pockets of a package tape having fixed dimensions. The coils do not move or rotate in the pockets. In other words, when one type of a package tape having pockets suited to a fixed height and a fixed width of air-core coils is prepared, the air-core coils are prevented from rotating and moving in the pockets, positively allowing the coils to be taken out by an automatic mounting machine.
In the surface-mount air-core coil described above, the cross section of the coil body perpendicular to the axis thereof may be formed of two opposing substantially semicircular sections and substantially straight sections connecting to the substantially semicircular sections. Since the coil body has a flattened shape, the coil has a low profile even with the same inductance. Therefore, an electronic component having this air-core coil and a communication apparatus having this air-core coil can be made to have a low profile. Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.